The number of applications using radio frequency energy is large and rapidly increasing. From wireless communications systems (voice and data) and wireless internet applications to automobile collision avoidance systems, the airwaves are filled with radio frequency signals for performing various functions. Because of the great number of radio frequency systems in operation, interference between systems is not uncommon. This interference can cause a decrease in the performance of one or more of the systems involved (such as an increase in the bit error rate of a communications system) and, therefore, should be avoided. One way to avoid such inter-system interference is to carefully plan the assignment of frequencies to the various systems so that nearby systems do not use similar or overlapping frequency bands. However, because many of today's radio frequency applications are non-stationary (i.e., mobile) applications, planning based on the physical location of the systems is difficult if not impossible. Another option is to assign a completely different frequency band to each application so that there is no frequency overlap between systems. This technique is not practical, however, because there is not enough spectrum available to service the growing number of RF applications in this fashion. In addition, this technique does not address interference caused by the transmission of spurious "out of band" signals, such as those created by system nonlinearities (e.g., amplifier intermodulation distortion), that create adjacent channel interference.
In addition to unintentional interference between systems, as described above, there is also the problem of intentional interference (i.e., jamming). This type of interference generally occurs in military applications where one group attempts to interfere with the communications of an enemy group by transmitting signals in a similar frequency range as the enemy group to block or overpower the communications signals. As can be appreciated, such interference can seriously degrade or destroy the quality of the communications.
Therefore, a need exists for a method and apparatus for use in a communications system that is capable of reducing the effect of interference on the data signal or existing signals.